1. Field of the Invention
The present invention relates to an enclosed wrench, and more particularly to such a wrench having an ability of reducing the sum of tolerance of the wrench and that of a working piece (such as bolts and nuts) to be driven (namely reducing the clearance between the wrench and the working piece to be driven), furthermore, which is capable of driving the deteriorating working pieces.
2. Description of the Prior Arts
A conventional enclosed wrench 10 (here takes a multi-point box-end wrench as example as shown in FIG. 1) has a drive head 11 defined at an end. On the internal surface of the drive head 11 a plurality of drive protrusions 13 are disposed, the drive head 11 serves to engage with the working piece to be driven the drive protrusions 13 confining the same. However, there are some disadvantages will be caused in real operation as follows:
First, as shown in FIG. 2, an enlarged view of quarter of the FIG. 1, the key structure of the conventional wrench 10 is that a predetermined number of tangent points 14, turning points 15 and arcs 16 should be disposed on the internal surface 12 of the drive head 11. However, the locations of the respective tangent points 14, turning points 15 and arcs 16 only can be figured out by complicated calculations, thereby caused difficulties in production.
Second, as shown in FIG. 3, another conventional wrench 20 is shown having a drive head 21 engaged with a corresponding sized working piece 22, in case of rather great clearances existing between the drive protrusions 23 of the wrench 20 and the respective side surfaces 24 of the working piece 22 to be driven that is deteriorating engagement, thereby the wrench 20 or the working piece 22 even maybe both of them will be spoiled during operation. If turns the wrench 20 by force, (as shown in FIG. 4), then the working piece 22 will be deformed and may not be driven. However, the wrench 20 is inapplicable to the deteriorating working piece 22, such that inconveniences are caused.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional enclosed wrench.